A curved lens will exhibit astigmatism effects when the object and the viewer are both off-center from the optical axis. When the object is a wide-angle reflective surface presenting an array of light-generating pixels to the eye, the astigmatism is particular to each location on the surface, and there will be both different amounts of astigmatism and different angles of incidence of the rays of light causing the astigmatism angle to vary across the field of view of the user.
The standard method of correcting astigmatism involves applying a cylindrical curvature to the lens such that it causes the sagittal and the tangential light fans to come to a real image focus at the same point in space. The cylindrical curvature is uniformly applied to the entire lens area, where the cylindrical curvature can be defined by an equation.